🛺 Pull-back Trike: step-by-step build

A three-wheeler with a spring engine — twist the front wheel and it drives in circles!

Tuk-tuks zoom around cities with three wheels: two at the back and one at the front. Your trike has a spring engine on the back axle and a single front wheel on a swivelling fork. Before you let go, twist the front wheel: straight ahead, a big circle, or a tiny circle — you choose! The spring engine is held tight by six pins and two frames, so all its power goes into the wheels.

  • Level 2 of 5 (easy)
  • About 20 minutes
  • 9 steps, 27 parts
  • Powered by: Pull-back
  • Series: Gearbox & Drivetrain Cars

What you will learn

  • Stored Energy: Energy can be saved up in a spring and let out later.
  • Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
  • Steering: Turning the front wheels makes a car follow a curve.
  • Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.

Build these first

  • Pull-back Racer🏁 Pull-back Racer: Pull it back, let it go — ZOOM! A racer with a spring for an engine. (level 2 of 5, about 12 minutes, 10 steps)

Parts you need

  • 1 × Pull-back motor
  • 1 × Axle 8
  • 6 × Black pin (grippy)
  • 2 × Open frame 5×7
  • 2 × Small white wheel
  • 3 × Axle 6
  • 4 × Cross block
  • 1 × Double cross block
  • 1 × Half bush
  • 2 × Blue long pin
  • 2 × L-beam 2×4
  • 1 × Axle 3
  • 1 × Thin-tyre wheel

Steps

  1. Take the pull-back motor — the spring engine — with its long body pointing forward. Push an 8-long axle through the cross hole at the bottom.
  2. Push a black pin half-way into the front one of the two top holes of the motor, and one into the first and the last hole of its bottom row — all on this side. Press an orange 5×7 frame onto the three pins, long side along the motor.
  3. Turn the motor round and do the same on the other side: three black pins half-way in, then the second frame.
  4. Push the two back wheels onto the motor axle.
  5. Slide a 6-long axle through the middle hole of the frames' front ends, with a cross block in the middle (free hole pointing down, in front of the axle) and a double cross block standing up beside it.
  6. Slide a second 6-long axle through the top holes of the frames and the top of the double cross block, with another cross block in the middle, free hole pointing down.
  7. The kingpin: hold two cross blocks under the front, one on top of the other, free holes pointing forward. Push a 6-long axle down through both top blocks into them, and put a half bush on its top end. The kingpin and these blocks turn together when you steer.
  8. Push a blue long pin through the free hole of each lower cross block, and press an L-beam onto each side — short leg down, long leg pointing forward. These are the fork legs.
  9. Push a 3-long axle through the front ends of the fork with the thin front wheel in the middle.

Play time

Point the front wheel straight, pull back and let go. Then twist it and try to make the trike drive a full circle and come back to you!

Real-world inspiration

Delta tricycles and tuk-tuks — https://en.wikipedia.org/wiki/Auto_rickshaw ; Rebrickable "Simple Pullback Vehicle" MOC-137777 — https://rebrickable.com/mocs/MOC-137777/TheAlternateBuilds/simple-pullback-vehicle/